.TH MPI_Sendrecv 3 "7/27/2010" " " "MPI"
.SH NAME
MPI_Sendrecv \-  Sends and receives a message 
.SH SYNOPSIS
.nf
int MPI_Sendrecv(void *sendbuf, int sendcount, MPI_Datatype sendtype, 
                int dest, int sendtag,
                void *recvbuf, int recvcount, MPI_Datatype recvtype, 
                int source, int recvtag,
                MPI_Comm comm, MPI_Status *status)
.fi
.SH INPUT PARAMETERS
.PD 0
.TP
.B sendbuf 
- initial address of send buffer (choice) 
.PD 1
.PD 0
.TP
.B sendcount 
- number of elements in send buffer (integer) 
.PD 1
.PD 0
.TP
.B sendtype 
- type of elements in send buffer (handle) 
.PD 1
.PD 0
.TP
.B dest 
- rank of destination (integer) 
.PD 1
.PD 0
.TP
.B sendtag 
- send tag (integer) 
.PD 1
.PD 0
.TP
.B recvcount 
- number of elements in receive buffer (integer) 
.PD 1
.PD 0
.TP
.B recvtype 
- type of elements in receive buffer (handle) 
.PD 1
.PD 0
.TP
.B source 
- rank of source (integer) 
.PD 1
.PD 0
.TP
.B recvtag 
- receive tag (integer) 
.PD 1
.PD 0
.TP
.B comm 
- communicator (handle) 
.PD 1

.SH OUTPUT PARAMETERS
.PD 0
.TP
.B recvbuf 
- initial address of receive buffer (choice) 
.PD 1
.PD 0
.TP
.B status 
- status object (Status).  This refers to the receive operation.
.PD 1

.SH THREAD AND INTERRUPT SAFETY

This routine is thread-safe.  This means that this routine may be
safely used by multiple threads without the need for any user-provided
thread locks.  However, the routine is not interrupt safe.  Typically,
this is due to the use of memory allocation routines such as 
.I malloc
or other non-MPICH runtime routines that are themselves not interrupt-safe.

.SH NOTES FOR FORTRAN
All MPI routines in Fortran (except for 
.I MPI_WTIME
and 
.I MPI_WTICK
) have
an additional argument 
.I ierr
at the end of the argument list.  
.I ierr
is an integer and has the same meaning as the return value of the routine
in C.  In Fortran, MPI routines are subroutines, and are invoked with the
.I call
statement.

All MPI objects (e.g., 
.I MPI_Datatype
, 
.I MPI_Comm
) are of type 
.I INTEGER
in Fortran.

The 
.I status
argument must be declared as an array of size 
.I MPI_STATUS_SIZE
,
as in 
.I integer status(MPI_STATUS_SIZE)
\&.


.SH ERRORS

All MPI routines (except 
.I MPI_Wtime
and 
.I MPI_Wtick
) return an error value;
C routines as the value of the function and Fortran routines in the last
argument.  Before the value is returned, the current MPI error handler is
called.  By default, this error handler aborts the MPI job.  The error handler
may be changed with 
.I MPI_Comm_set_errhandler
(for communicators),
.I MPI_File_set_errhandler
(for files), and 
.I MPI_Win_set_errhandler
(for
RMA windows).  The MPI-1 routine 
.I MPI_Errhandler_set
may be used but
its use is deprecated.  The predefined error handler
.I MPI_ERRORS_RETURN
may be used to cause error values to be returned.
Note that MPI does 
.B not
guarentee that an MPI program can continue past
an error; however, MPI implementations will attempt to continue whenever
possible.

.PD 0
.TP
.B MPI_SUCCESS 
- No error; MPI routine completed successfully.
.PD 1
.PD 0
.TP
.B MPI_ERR_COMM 
- Invalid communicator.  A common error is to use a null
communicator in a call (not even allowed in 
.I MPI_Comm_rank
).
.PD 1
.PD 0
.TP
.B MPI_ERR_COUNT 
- Invalid count argument.  Count arguments must be 
non-negative; a count of zero is often valid.
.PD 1
.PD 0
.TP
.B MPI_ERR_TYPE 
- Invalid datatype argument.  May be an uncommitted 
MPI_Datatype (see 
.I MPI_Type_commit
).
.PD 1
.PD 0
.TP
.B MPI_ERR_TAG 
- Invalid tag argument.  Tags must be non-negative; tags
in a receive (
.I MPI_Recv
, 
.I MPI_Irecv
, 
.I MPI_Sendrecv
, etc.) may
also be 
.I MPI_ANY_TAG
\&.
The largest tag value is available through the 
the attribute 
.I MPI_TAG_UB
\&.

.PD 1
.PD 0
.TP
.B MPI_ERR_RANK 
- Invalid source or destination rank.  Ranks must be between
zero and the size of the communicator minus one; ranks in a receive
(
.I MPI_Recv
, 
.I MPI_Irecv
, 
.I MPI_Sendrecv
, etc.) may also be 
.I MPI_ANY_SOURCE
\&.

.PD 1

.SH LOCATION
sendrecv.c
